There has been a recent trend toward telecommunication network architectures having switching nodes decomposed into call control functionality and bearer control functionality. It will be recognised by those skilled in the art that various call control functions and bearer control functions are known, and those functions may be effected by computer software programs residing within one or more telecommunication network nodes. With the decomposition of switching nodes into the call control functionality and the bearer control functionality, a vertical control protocol is required for communication between the respective call control and bearer control functions. An example vertical control protocol is the Media Gateway Control Protocol which enables external control and management of Media Gateways by Media Gateway Controllers. Media Gateway Control Protocol messages convey the control and management information between the MGC and the MG. MGs typically operate at the edge of multi-service packet networks and examples of MG devices include voice over IP Gateways, voice over ATM Gateways, modem banks, cable modems and set top boxes. The call control and bearer control functions are equally applicable to a situation where call control function resides within a Media Gateway Controller (MGC) or a Call Serving Function such as CSF, CSM, or CSN, and bearer control function resides within a Media Gateway (MG) or a Bearer Interworking Function such as BIWF, BCF, or BCU.
It will also be recognised by those skilled in the art that a bearer is a connection that carries the user plane information of a call. For example, a bearer may be an ATM (Asynchronous Transfer Mode) connection carrying a voice call or an IP (Internet Protocol) connection carrying a data call. In the instance of a decomposed switching node, the bearer control function manages the establishment, modification and release of physical bearers for a call. At the time of call establishment, the call control function requests the bearer control function to establish a call using bearers with characteristics that satisfy the requirements of the call. Bearer characteristics relate to the physical characteristics of the bearer, for example, bandwidth, packetisation, packet size, coding type, or framing.
At various times, a modification to the characteristics of the bearers in an established call connection may be required or requested. However, the bearer control function does not generally support bearer modification signalling and in the event that bearer modification signalling is supported, the call control function is generally unaware of this capability. In this respect, the capability of the bearer control function refers to the capability of the bearer control protocol associated with a bearer. For example, whether the bearer may have its characteristics modified or whether it has release procedures depends upon the capabilities of the associated bearer control function. For whatever reason, if a request to modify the characteristics of a bearer cannot be accommodated by the associated bearer control function, an error message is typically sent from that entity effecting the bearer control function to the entity effecting the call control function indicating that the request cannot be satisfied.
In existing systems, an error message in response to a request from a call control function to modify the characteristics of a bearer typically does not indicate the precise reason for the error. In some instances, the bearer control function may support a modification signalling protocol but the error message may be sent for another reason such as congestion.
Upon receiving an error message from an entity effecting a bearer control function, the call control function may attempt to satisfy a modification request by seeking to establish an alternative bearer connection with alternate bearers having appropriate characteristics.
However, the time delay associated with the process described above in attempting to satisfy a request to modify the characteristics of the bearers in an established call connection is significant and substantially increases the risk of a timeout, which causes the existing call connection to be dropped, as a result of the modification request not being satisfied within time constraints. Further examples of this problem are dropped or delayed packets, producing silences or clicking that may be perceived in a call. All these effects contribute to an unsatisfactory performance of the network.
As a result, it will be recognised by those skilled in the art that the call control function cannot manage a smooth and efficient modification to bearer characteristics for an established call connection with a reasonable probability of achieving the modification within required time constraints.
It is an object of the present invention to ameliorate or overcome one or more disadvantages of the prior art.
It is another object of the present invention to provide an improvided system and method of responding to requests for a modification to bearer characteristics such that the improvement enables a determination as to the ability to satisfy the request to be ascertained and/or effected with greater efficiency as compared with existing systems and methods.